1. Field
The present invention relates to an apparatus and method for managing battery power in a portable device having at least one battery pack mounted therein, and more particularly, to an apparatus and method for managing power of battery packs in a portable device, in which the charging and discharging order is selectively controlled according to a value of a charging current of each battery pack electrically connected to the portable device thus to increase the power use efficiency of the battery packs.
2. Description of Related Art
With the development of electro-communication technology, devices such as personal computers (hereinafter, referred to as “PCs”) have been made portable. For example, portable electronic devices, such as notebook PCs, personal digital assistants (PDAs), have a small size or lightweight in consideration of mobile environments, i.e., portability for use in outdoor places.
A notebook PC is characterized in a “battery driving type,” that is, the notebook PC is driven by a built-in battery as well as by a commercial AC power source using an AC adaptor. This allows the notebook PC to be used at places such as outdoor places and business trip places where the commercial AC power source is unavailable. In general, the built-in battery is in the form of a battery pack having a plurality of battery cells packaged. A typical battery cell is a rechargeable cell, such as a Li-Ion or NiMH cell.
A battery built in or coupled to a notebook PC has a limited capacity. The duration of a once fully charged battery depends on the number of cells and a system specification but is only about 3 to 4 hours. Accordingly, researches have been studied to extend the duration of a portable device by a battery.
A so-called “power management” related technique is the best example for extension of battery duration. It is known that the duration can be extended by increasing the number of cells in a battery pack or using a cell having high energy density such as a lithium-ion cell. However, if the number of the cells in the battery pack is increased, the weight and size of the battery pack is also relatively increased, which does not allow the number of the cells in the battery pack to be only increased.
In recent years, a notebook PC of a “dual battery” type in which two battery packs can be built in or coupled to the notebook PC has been developed and manufactured. For example, a computer system of a dual battery type is disclosed in Japanese Patent Laid-open Publication No. HEI 8-54967 filed by “International Business Machines Cooperation.” Further, a notebook PC “TX4210K” in the “XNOTE TX series” (XNOTE is a trademark of LG Electronics Inc.) available from LG Electronics Inc. has a structure in which an optional battery pack is detachably coupled to a back plane of the computer.
In addition to the notebook PCs, launched are portable devices having a battery pack named as a subsidiary or optional battery, which is exchanged for a floppy disc drive (FDD), optical disk drive (ODD) or the like detachably coupled to the portable devices. A portable device having two battery packs has a doubled duration in comparison with a portable device having one battery pack. Of course, the duration depends on the number of optional batteries added to a portable device in addition to a basic battery pack.
A notebook PC having dual battery packs includes a power management unit for setting the discharging/charging order of basic and optional battery packs so as to efficiently manage the power from the dual battery packs. The power management unit of the notebook PC preferentially discharges the built-in or mounted optional battery pack to drive the computer and then discharges the basic battery pack when the optional battery pack is substantially almost discharged. When the battery packs are charged by the external power supplied via an AC adaptor, the power management unit of the notebook PC controls a computer system to charge the basic battery pack voltage earlier than the optional battery pack. When it is detected that the basic battery pack is fully charged, the power management unit controls the computer system to charge the optional battery pack voltage.
The charged optional battery pack is preferentially discharged and the basic battery pack is preferentially charged to enable the portable device to be driven by the built-in battery even when the optional battery is detached from the portable device since the optional battery is mounted as an external device to the portable device or coupled to the portable device in a place from which an FDD, an ODD, or the like is detached.
However, with the conventional method for managing power of the battery packs in the portable device of a dual battery type in which the charging and discharging order is set so that the optional battery pack is preferentially discharged and the basic battery pack is preferentially charged, it takes much time to charge the battery packs as the discharging and charging operation is performed in the predetermined order of the basic and optional battery packs irrespective of charge capacities of the battery packs.
A charging time of a general battery pack is known to be in proportion to a battery use ratio (a used capacity relative to a total capacity). For example, it can be discovered that in a general notebook PC, if two battery packs having different capacities are discharged and then charged under the same condition, a charging time of the battery having a smaller charging capacity is longer than that of the battery having a greater charging capacity. This is because a charge control circuit of the notebook PC supplies a voltage terminal of the battery pack with a charging voltage with a current capacity adjusted to a charging current of the battery pack.
In the notebook PC, the charge control circuit is designed to output a charging voltage with a relatively high current capacity, and adjusts a current capacity of a charging voltage supplied to the voltage terminal of the battery pack according to a charging current of the battery pack. For this operation, the charge control circuit of the notebook PC acquires information on the charging current capacity from the battery pack to be charged via a system management (SM) bus, and supplies the voltage terminal of the battery pack with the charging voltage corresponding to the charging current of the corresponding battery pack in order to charge the battery cell.
Accordingly, it can be seen that the charging time of the battery pack of the notebook PC is not in proportion to a discharged amount of the battery but is in proportion to a used capacity relative to a total capacity of the battery, i.e., a battery use ratio. When the capacity of the basic battery pack is greater than that of the optional battery pack, the conventional method for managing battery power of the notebook PC preferentially discharges the optional battery pack irrespective of a battery capacity. In this case, it takes much time to charge the battery pack in comparison with a case where a battery pack having a greater battery capacity is preferentially discharged and charged. When the capacity of the basic battery pack is smaller than that of the optional battery pack, the conventional method for managing battery power preferentially charges the basic battery pack having a smaller battery capacity, so that the same charging time is consumed but a charging effect lowers as compared with a case where a battery having a greater charging capacity is charged preferentially.
As described above, in the conventional method for controlling the charge and discharge of dual battery packs, according to the predetermined order irrespective of charging and discharging characteristics of the battery packs, the optional battery pack is discharged earlier than the basic battery pack, and the basic battery pack is charged earlier than the optional battery pack when an external AC power source is supplied. Accordingly, there is a problem in that it takes much time to charge the battery packs when the capacity of the optional battery is smaller than that of the basic battery.